InnoDB 1.1 combines the familiar reliability and performance of the
InnoDB storage engine, with new performance and usability
enhancements. InnoDB 1.1 includes all the features that were part of
the InnoDB Plugin for MySQL 5.1, plus new features specific to MySQL
5.5 and higher.

Beginning with MySQL version 5.5, InnoDB is the default storage
engine, rather than MyISAM. As of MySQL 5.5, issuing the
CREATE TABLE statement without an
ENGINE= clause creates an
InnoDB table.

InnoDB tables arrange your data on disk to
optimize queries based on
primary keys. Each
InnoDB table has a primary key index called
the clustered index
that organizes the data to minimize I/O for primary key lookups.

To maintain data
integrity,
InnoDB also supports
FOREIGN
KEY constraints. Inserts, updates, and deletes
are all checked to ensure they do not result in inconsistencies
across different tables.

You can freely mix InnoDB tables with tables
from other MySQL storage engines, even within the same
statement. For example, you can use a
join operation to combine data
from InnoDB and
MEMORY tables in a single query.

InnoDB has been designed for CPU efficiency
and maximum performance when processing large data volumes.

The InnoDB storage engine maintains its own
buffer pool for caching data
and indexes in main memory. When the
innodb_file_per_table setting is
enabled, each new InnoDB table and its associated
indexes are stored in a separate file. When the
innodb_file_per_table option is
disabled, InnoDB stores all its tables and
indexes in the single system
tablespace, which may consist of several files (or raw disk
partitions). InnoDB tables can handle large
quantities of data, even on operating systems where file size is
limited to 2GB.

InnoDB Enhancements and New Features

The InnoDB storage engine in MySQL 5.5 releases
includes a number performance improvements that in MySQL 5.1 were
only available by installing the InnoDB Plugin. This latest InnoDB
(now known as InnoDB 1.1) offers new features, improved performance
and scalability, enhanced reliability and new capabilities for
flexibility and ease of use. Among the top features are Fast Index
Creation, table and index compression, file format management, new
INFORMATION_SCHEMA tables, capacity tuning,
multiple background I/O threads, multiple buffer pools, and group
commit. For more information about these features, see
Section 14.1.1, “Features of the InnoDB Storage Engine”.

For additional information about InnoDB
enhancements and new features in MySQL 5.5, also refer
to: